After quarters of confounding Wall Street "expert" analysts with better-than-expected earnings, could Apple, Inc. (AAPL) be on the verge of a highly uncharacteristic miss of its own earnings target? That's what Citigroup Inc. (C) analyst Glen Yeung predicted in his research note, citing supplier information as pointing to weaker-than-expected iPhone and iPad sales.

That prediction has been boosted by Cirrus Logic Inc. (CRUS), which provides audio chips for the iPhone and iPad. Cirrus warned investors Wednesday in its fiscal fourth quarter earnings results that its margins had weakened and that it was taking a large charge on unsold inventory of audio chips.

Cirrus's chip stock fluctuates primarily with the sales of its largest customer Apple's devices. Thus the large stock of unsold chips indicates weak sales of Apple's flagship devices.

Since the passing of iconic leader and late CEO Steven P. Jobs, Apple has continued to grow steadily under the quiet leadership of new CEO Tim Cook, but some fear the company is losing its marketing luster. Apple's faces tough competition from Android rivals -- particularly Samsung Electronics Comp., Ltd. (KSC:005930) and Google Inc. (GOOG) -- who have been more aggressive in updating their products' hardware and software.

Apple, which last year bumped the screen size of its iPhone to 4-inches, has largely been coasting on a "if-it-isn't-broken-don't-fix-it" approach to its operating system. While sales were strong last quarter, investors hammered the company's stock, concerned about weakening margins (profitability).

For a while it looked like $420 was a solid floor that the stock would resist breaking through. But amid the supplier warning Apple's stock plunged briefly below $400 USD. It is currently trading around $403 USD. Apple has lost over a quarter trillion dollars in market capitalization over the last half year, since hitting a record $700 USD per share last September.

Overall, the tech sector was down on Wednesday, but Apple's stock sunk more than most, dipping over 5 percent on the bad news. Rival Google Inc.'s (GOOG) stock is trading around $780 USD, down ~1.5 percent. Google's market capitalization is currently around two-thirds that of Apple, as its stock hovers around record highs of $800 USD per share.

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